Why is "uncanny" not the opposite of "canny"?

If canny means "cunning"

Having or showing shrewdness and good judgement, especially in money or business matters.

why does uncanny mean "supernatural"?

Strange or mysterious, especially in an unsettling way.

Uncanny should have meant "slow-witted" or "foolish" which is the opposite of cunning.

Uncanny:

• 1590s, "mischievous;" 1773 in the sense of "associated with the supernatural," originally Scottish and northern English, from un- (1) "not" + canny.

• Canny is from the Anglo-Saxon root ken: "knowledge, understanding, or cognizance; mental perception: an idea beyond one's ken." Thus the uncanny is something outside one's familiar knowledge or perceptions.

(Etymonline, Wikipedia)

Also from The Word Detective:

• “Canny” is a very cool word. It first appeared in Scots and Northern English dialects as an adjective meaning “knowing, judicious, prudent, cautious,” and is simply based on the verb “can” in the sense of “to be able” (as in “I can fly”). “Canny” was picked up by English writers in the 17th century, who applied it to the Scots themselves in the sense of “cunning,” “wily” or “thrifty,” in line with the English portrayal of Scots as clever and frugal. The sense of “sharp” and “shrewd” eventually became more generalized, and today we use “canny” to mean “perceptive and wise” (“The canny investor avoids market fads”).

• One of the other meanings of “canny” back in Scotland in the 16th century, however, was “trustworthy,” and when “uncanny” first appeared it was in the sense of “malicious or incautious” (i.e., not trustworthy). By the 18th century, “uncanny” had come to mean specifically “not safe to trust because of connections to the supernatural,” and eventually the word took on its modern meaning of “supernatural,” “weird” and “strange.” So “uncanny” came to mean something quite different than simply “not smart.”